The present invention relates to spandrel glass window film containing metallic flakes. More particularly, it refers to the manufacture of multilayered thin film at least one layer laminated together to an adjacent layer by a laminating adhesive containing dispersed encapsulated metal flakes.
In the window film market problems have arisen in attempting to coat a roll of defect free film using rod, slot die, reverse roll or reverse gravure coating technology.
For long term stability in water based coatings it is known to provide silica encapsulatd aluminum flakes or gold bronze flakes. Encapsulation of the metallic flake has been attempted as shown in U.S. Pat. No. 5,037,475. Encapsulation enables metallic pigments to be uniformly dispersed in a resin system, but that alone does not create defect free film for use as a safety film to provide impact resistance to glass.
Metallic pigments have been used in coating for a long time. To overcome the compatibility problem, many dispersion agents are used to make “leafing” and “non-leafing” flakes. If the metallic flakes are covered with a hydrophobic layer of stearic acid, it causes a significant influence on the wetting properties and will drive the pigments, especially in waterborne systems, towards the coating's surface; i.e., leafing” effect. This “surface-oriented” alignment gives excellent brilliance and chroma, but the pigments are not fully embedded into the coating's film. Consequently, they have poor rub-resistance and are very sensitive to corrosion. The use of surfactants or polar organic solvents provides better wetting, hence pigments turn out to be “non-leafing”.
The metallic pigments have been widely used in car paint, consumer products, and construction coating. Based on all these properties, it would be desirable to apply the metallic pigments into window films. The brilliant sparkle effect is a result of large metallic flake orientation. These large particles, unfortunately, cause many coating difficulties. Using traditional coating methods such as rod, slot die, reverse roll and reverse gravure causes coating streaks and pin-holes because of the metallic flake agglomeration. Using dispersion agents can ameliorate the agglomeration but cannot eliminate such agglomeration. When settling occurs, the pigments can form a solid flocculated mass that is often difficult to re-suspend. This small portion of agglomeration can cause significant coating streaks with all the above coating methods. Smaller particles cause less coating streaks but give less desirable appearance. It does not have the brilliant sparkle effect but appears like a dull paint.
A process is needed that will produce a defect free multi-layered film that will provide a safety protective coating to glass with desirable color brilliance.